Which aircraft is on standby for air-to-air refueling support in UK operations?

The Voyager is the correct choice as it is specifically designed for air-to-air refueling and has been integrated into UK operations for this purpose. The Voyager, which is a modified version of the Airbus A330, serves as the Royal Air Force's primary air refueling tanker. It plays a critical role in extending the operational range of fighter aircraft and supporting various missions, making it indispensable for sustained air operations.

In contrast, while the Typhoon and F-35 Lightning are both advanced combat aircraft capable of engaging in various missions, they are not dedicated refueling platforms. The C-17 Globemaster, meanwhile, is a strategic transport aircraft, primarily used for transporting troops and cargo rather than conducting refueling operations. Therefore, the Voyager stands out as the designated aircraft for air-to-air refueling support.